Proceedings of The Physiological Society

University of Cambridge (2004) J Physiol 555P, C85

Communications

The cardiovascular changes associated with warming and cooling in the turtle, Trachemys scripta

Gina L. J. Galli, Tobias Wang* and E. W. Taylor

*Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark and School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK


The cardiovascular changes associated with warming and cooling were investigated in seven freshwater turtles, Trachemys scripta. Animals were anaesthetised by isoflurane inhalation, a piece of the ventral carapace over the heart was removed with a bone saw, and blood flow probes (Transonic Systems Inc.) were placed around the left aortic arch and left pulmonary artery. The carotid artery was occlusively cannulated, using a PE50 catheter, for blood pressure measurements. Animals were then artificially ventilated until spontaneous ventilation resumed, and allowed to recover for a period of 48 hours. The turtles were warmed to 34 °C, using an infrared 150W heating lamp, and then allowed to cool to 24 °C, both before and 45 min after intrarterial injection of atropine (3 mg kg-1). All experimental animals were humanely killed following the protocol using an overdose of Pentobarbitol (intrarterial injection of 200 mg kg-1).

All turtles warmed at a faster rate than they cooled. Animals exhibited a hysteresis of heart rate and blood flow to both the pulmonary and systemic circulations, which was not cholinergically mediated (Fig. 1A). Blood pressure remained constant during both warming and cooling (Fig. 1B), while systemic resistance decreased during heating and increased during cooling, indicating a barostatic response. Hicks (1998) described a large R-L shunt in Trachemys scripta which increased with heating and decreased with cooling in untreated animals, interpreting the shunt pattern as a passive consequence of altered resistances within the systemic circulation. However, in the present study, there was a large R-L shunt during warming and cooling in untreated animals which remained relatively constant. This may indicate an active regulation of cardiac shunts in order to sustain oxygen delivery. Atropinisation resulted in a large L-R shunt which decreased during warming and increased during cooling. However, the cooling periods were extended in atropinised animals, indicating that heat lost across the lung surface is not a determining factor in rates of cooling.

Where applicable, experiments conform with Society ethical requirements